In a known conventional GSM system, each mobile station, such as a mobile telephone handset, is provided with a SIM, also referred to as a smart card, which is inserted into the mobile station in order to allow the mobile station to receive service in a GSM network.
The SIM includes a microprocessor, memory elements including a permanent memory (e.g. ROM), a non-volatile re-writable memory (e.g. EEPROM) and a volatile re-writable memory (e.g. RAM), and contacts for forming the data transfer interface between the SIM and the mobile station.
A set of SIM-based data records are defined in the GSM standard. These include permanent data records, such as that holding the international mobile subscriber identity (IMSI) whereby a mobile subscriber is recognised by a mobile communications network. Other data records are modifiable, either at the initiative of the mobile station, such as the data record holding the current location area information (LAI) for the mobile station, or at the initiative of the mobile subscriber, such as a set of fixed dialling number (FDN) records which are used to allow the subscriber to bar calling of, or restrict calling to, the dialling numbers stored in the set of FDN records.
The GSM standard also specifies a command set for use by a mobile station to access data record in the SIM and retrieve and write data items from and to the file. Each standard data record has a standard data record address which is specified in an access command for that data record sent by the mobile station. The SIM uses the data record address in order to determine which data record is to be accessed. Thus, there is a linear relationship between a data record access command sent by the mobile station and the data record accessed by the SIM.
Thus, in theory any standard GSM mobile station is compatible with any standard GSM SIM which is connectable to the mobile station. Any basic GSM feature implemented on the mobile station which involves the storage and/or retrieval of the contents of a standard data record in the SIM is obtainable. Furthermore, by use of a standard such as the GSM standard, manufacturers are able to lower the cost of the technology involved, by pooling the cost of research and development. Production costs can also be minimised by a manufacturer by the use of basic designs which can be modified for the supply of equipment to different GSM network operators. Individual features for specific GSM operators can thus be provided on the equipment, whilst the basic GSM features are provided as a matter of course.
A subset of GSM mobile stations and SIMs are used in PCN (Personal Communication Network) Networks. PCN mobile stations and SIMs comply with the GSM/DCS 1800 standard. An added dual-line mode feature allows the mobile station to operate in two different line modes. A different dialling number (MSISDN) is associated with each mode, and stored in the SIM. The mobile station still retains only a single IMSI with which both MSISDNs are associated. The particular MSISDN for which a voice call is made is signalled on the network/mobile station radio interface by means of a bearer service code. For outgoing calls the signalled bearer service code is logged by the network in order to make an appropriate record of the call, e.g. for billing purposes, against the appropriate MSISDN. For incoming calls, the mobile station notes the signalled bearer service code and retrieves the corresponding MSISDN from the SIM and displays the MSISDN, or an associated line identifier, to the user when indicating the receipt of an incoming call.
European patent publication number EP-A-0526981 describes a cellular radio telephone which has two or more directory numbers stored in a memory. In one mode of operation, all of the directory numbers are enabled for incoming calls. In another mode of operation, one of the directory numbers is disabled such that the telephone will not respond to an incoming call intended for that number. Other modes may be provided where other of the directory numbers are disabled. When an incoming call is received, a microprocessor of the telephone compares the telephone number for which the incoming call is intended with each of its stored numbers. Providing the stored number is enabled, the telephone call is signalled to the user and the call may be answered in the conventional way. The directory numbers are stored in the memory in a conventional way, that is to say the directory numbers are stored as a set of records, each one of which may be independently addressed by the microprocessor.
International patent publication number WO 92/19078 describes a GSM-type mobile telephone system in which a smart card is allocated two IMSIs which are selectively activated by the user. Two SIM circuits are located at different ends of the smart card and are selectively activated by inserting the smart card into the mobile station in one of two ways. Each of the SIM circuits is provided with a different IMSI. Once the smart card is inserted into the mobile station, the mobile station accesses a data record, such as the IMSI data record, in a conventional fashion, and the data presented to the mobile station can be altered by removal and reinsertion of the smart card in an inverted disposition. A similar effect could be achieved simply by providing two separate SIMs having different subscriber identities. The SIM is in effect two SIM circuits combined on a single smart card.
According to one aspect of the present invention there is provided a removable data store for a user interface device, said data store comprising a memory for storing data, which memory is accessible by access procedures controlled by memory access messages sent by said user interface device, said data store further comprising a processor circuit having a first response to a memory access message, and a second response, different to said first response, to said memory access message, wherein said processor circuit independently selects between said first response and said second response on the basis of a current operational condition of said user interface device.
In the conventional arrangements, when a feature is to be added to the user interface device, such as a user station for a mobile communications system, which involves the storage and/or retrieval of data from the removable data store, such as a SIM, both the user station and the SIM must be modified. A new type of data record must be defined on the SIM having a new data record address by which the user station can address the data record. The user station itself must be provided with a new data record access procedure, involving the use of the new data record address on the SIM, for accessing the new data record.
One advantage of the present invention is that it provides an alternative method of providing a new feature, in which different responses are given to a memory access message sent by a user station. Implementation of the new feature does not necessarily require modification of the user station itself. The new feature can be implemented on the SIM, or equivalent data store, and activated in response to determination by the SIM as to which mode of operational condition of the user station, or other user interface device, is current.
Furthermore, when a feature involving access to a new data record on the SIM is added according to the conventional method by the modification of the SIM and the user station, a loss of inter-compatibility of the SIM with other user stations is inevitable. The added feature cannot be obtained when the modified SIM is inserted into a different user station, which otherwise complies with the same standard. Thus, use of the added feature is restricted to a combination of user station having the added feature capability and a SIM also having the added feature capability.
Another advantage of the present invention is that inter-compatibility of a data store with any standard user interface device can be retained. The added feature can be implemented solely on the data store, and invisibly to the user interface device, by arranging that the removable data store can independently determine whether the user interface device is in one operational condition or another.
In the past, only one data record has been accessible on a removable data store, such as a SIM, in response to a data record access message sent by a user interface device, whichever operational condition the user interface device is in. In the present invention, the data store is able to respond by the retrieval of data from alternative memory portions, depending on the operational condition of the user interface device. Data records specific to one operational condition can be stored and/or retrieved selectively in accordance with the operational condition of the user interface device.
In one type of known SIM, a data record is allocated for the storage of data relating to the mode of operation of a mobile station. Namely, a line flag record is already provided in some PCN SIMs, in particular those of the present applicant, to provide a PCN mobile station with a non-volatile record of the previously operative line after the mobile station has been switched off. When a line mode is chosen by the user, the mobile station writes the appropriate data into the line flag record, located at a predetermined memory address, using a SIM record update procedure. Then, when the mobile station is switched off and subsequently switched on, the mobile station performs a line flag record read procedure to determine which line mode to enter when the mobile station is initialising its various modes of operation. Thus, the line flag record has in the past been read only to determine a previous line mode of the mobile station, in order to set the line mode. The current line mode is not read